Regulated intramembrane proteolysis of the amyloid precursor protein (APP) leads to the production of Abeta, the causative agent in Alzheimer's disease (AD) and is therefore an important target for therapeutic intervention. However, there is a growing consensus that gamma-secretase, one of the enzymes involved in the generation of Abeta, is also involved in pathways critical for the signal transduction of Notch and a growing list of other receptors. It is becoming increasingly clear that an explicit understanding of the extent of the involvement of gamma-secretase in cellular processing and signaling pathways is necessary for the rational design of gamma-secretase inhibitor therapies in AD. APP is a member of a gene family that includes two amyloid precursor-like proteins, APLP1 and APLP2, however to date there is no data regarding details of the capacity of these proteins to act as competitive substrates for gamma-secretase. Here we propose 3 interrelated aims designed to generate detailed information about the ability of the APLPs to act as competitive substrates for gamma-secretase and to provide a better understanding of their biological role. We will determine the extent to which the APLPs can compete with APP for a series of gamma-secretase inhibitors that are currently being characterized and assessed for therapeutic use. We will also establish whether like APP, the APLP intracellular domains (ICDs) can translocate to the nucleus and whether the expression of members of the FE65 family have an effect on the stability or localization of these fragments. Finally, we will us microarray analysis in an effort to determine if there are specific genes whose expression is regulated by the translocation of the APP/APLP ICDs the nucleus. The experiments described in this application will be a valuable asset for understanding the biology of the APP/APLP gene family and ultimately the role they play in signaling pathways in the brain. Because the cleavage of APP by gamma-secretase is also linked to the production of Abeta, it is clear that the regulation of this event may be beneficial. It is likely that therapeutic alterations of gamma-secretase activity will effect the processing of APLP as well as that of APP, therefore it will be prudent and necessary to learn more about the functional role of the APLPs in order to assess the impact that gamma-secretase inhibition will have on normal brain function.